Highly-selective circuit



Y H. w. NICHOLS HIGHLY SELECTIVE CIRCUIT Y Filed Dsc. 5l 1921 Hara/dW/V/aa/sz f-)Aw Y El- Rece 1:12719 Cucu-u;

l I l I Il Mill Freyuency.

Patented Fein. id, i925.

U hl Vif E tenen ernten..

HAROLD W. NCELS, QF MAPLE'WGGD, NEW JERSEY, SSIGNOE TO 'WESTERN ELEC-TRG QOMPANY, INCREMTEU, F NEW' YORK., N. Y., .L CRPEATIN 0F NEW YORK.

HIGHLY-SELECTIVE CIRCUIT.

Application tiled December 3l, 1921. Serial No. 528,208.

To alt whom t muy concern lie it known that i, Honour) TVILLlAM Nichons,'a citizen of the United States, residing at Maplewood, in the county ofEssex, State of New Jersey, have invented certain new and usefulimprovements in HighlySelective Circuits, of which the following is afull, clear, concise, and exact description.

This invention relates to selective electric circuits and moreparticularly to networks for selecting a wave of desired frequency froma common medium or circuit carrying disturbing electrical energy.

It is old in the art to employ tuned circuits and lters for the purposeof selecting one particular frequency or bandv of frequencies from acircuit'carrying current of disturbing wave frequencies in order toobtain a high degree of discrimination between desired and vundesiredWaves. When high selectivity is required, however` ditiiculties areencountered in constructing capacity and inductance elements of therequisite constants, inasmuch as the dimensions of these elementsapproach prohibitively large values as the selectivity Iis increased.One object of this invcntionis to obtaina high degree .of selectivityWithout employing bulky or expensive capacities land inductances.

In accordance with the present invention a network comprisingdistributed -series and shunt impedance is connected to the Ysource ofelectric energy from which a particular wave frequency is to beselected. Two or more repeaters' are connected to said filter, thecontrol `element or gridof each repeater being connected to a dilerentpoint in said filter, these points beinp so chosen that, at the desiredfrequency, t ie potentials of said grids are in phase with each otherand cause the fiow through a common outputcircuit ot' currents lwhichsupplement each other. At any other frequencies thanthe desiredircrpiency. the potentials of the grids will he in ditl'erent phaserelation to each other and for this reason will produce currents in theoutput circuit of the repeaters which tend to neutralize each other. Thecommon out-put circuit of the repeaters is tuned to the frequency waveto be selected thus aidin in the discrimination between desired anundesired wave energy. A receiving circuit is coupled to the common outut circuit of the repeaters for the purnose c obtalmng a response from awave of desired frequcncy. This combination of the network and repeatersbesides being highly selective at sonne particular frequencydiscriminates betweenelectric impulses and' sustained waves, in view ofthe fact that impulses will in general excite free oscillations ofdifferent frequencies from that of the desired waves. Other objects ofthe invention will be apparent from the more detailed description of theinvention which follows, taken in view of the appended drawing andclaims.

Fig. 1 is a circuit diagram of a generic form of the invention. Fig. 2is a diagram illustrating a modification of the invention employing aiilter having distributed series inductances and shunt capacity. Fig. 3is a ,graph illustrating the selective characteristics of a circuitsimilar to Fig. 2. Fig. 4 is a modified form of the invention in whichthe filter comprises an aerial or antenna circuit.

Referring to Fig. 1, the source of electrical energy 1. comprises asource of sustained electric wares, and may also include a source ofelectric impulses. Source 1 may be an antenna, or a line wire such as asignal or power line. and is connected to one end of a network or bandfilter E2, comprising a plurality of series impedance elements 3, 4, 5,6, 7, etc., and shunt impedance elements 8, 9, 10, 11, 12. ctc.,theseimpedances being composed `of capacity, inductance, and resistance inthe relation called for in any wellknown type of filter, it beingunderstood that any one, or more, ofthe three constants of capacity.inductance, or resistance may be omitted from any given impedance. Theattenuation of the network Q. is preferably made very small, orsubstantially zero for waves of desired frequency. but it is to hedistinctly understood that'the principle of this invention may becarried out success fully when a filter or network havingr apprc- 100.ciable attenuation for the desired waves is used.

A lurality of repeaters lil. 14. 15, ctc.. each iiavifig a cathode 1G,an anode 17, and` 'a grid 18, are arranged 'with their output 105circuits in parallel and are supplied with space current from the commonsoprce 19. Cathodes 16 of the repeating devicesV are connected through acommon source of grid polarizing potential 20 andthe network 2 110 f thepotential st the to the grids 18, euch grid being connected to thenetwork 2 at e diii'erent point 21, 22, 23, etc. The Iiormul potentielsof the grids ere mede negative with respect to the cath odes 16 bythesource of potentiel 20. Points 2l, 22, .23, etc., are so chosen in thenetwork 2 that at some given Jfrequency which it is desired to receive,the potentiel waves et-these points will be other, angles of 360 degreesund integral multiples thereof `not being counted. in other Words, atthe desired frequency, if the potentiel et the point 2l be displaced inphase by a given ungle from the potentiel et the lower terminal oi thesource l, points 22 und 23 will be displaced from Suid potentiel at thesource l by seid angle. It Will, therefore, be seen that, et. thedesired. signal frequency, the same effect is produced on each of thegrids 18, essumingthet the network 2 hcs'zero attenuation for Waves ofdesired frequency. Uien use is mede of e network Wliich ep- .preciably'attenuetes the waves of desired requency, the amplification ot' therespective repeaters is adjusted to, compensate for the loss in weveamplitude caused by the network.

li or frequencies other than the signal frequency to be received, the inrpedunceJ elements 3, 4, 5, etc., 8, 9, 1G., etc., will in genl eralhave different phase angles, und for this fioA reason, at any one ofseid other frequencies, a weve of potentiel at the point 2l will be outof phase With the weve ot potential at point l22 While the Wave ofpotential at point 23 will be out of phase with the'waves of potentielat the points 2l und 22. it is to be noted that the points 2l, 22, 23,etc., are at different electrical distances from the source l.

utput circuit 25, including vinductuuce 26 und the variable capacity 27,is tuned to the frequency of the Waves to be received, fvlhiletunedcircuit 28 including,r veriuble capacity 29 and inductance 30 is tunedto .the saune frequency es circuit 25.

Circuit 28 connected to the input terminals of u 'detector or otherrepeating device 31 which 1s connected to the ret iving circuit inasmuches grids 1S receive potcntisi vu riutions in phase with euch other atthe desited frequency, while they receive potentiel variations out ci?pliese with esch other st iuidcsired frequencies, the space currentvariations of desired frequency will be in phase with each other in thetubes .13, le, etc., and will, therefore, coo erste to produce e maximumcurrent in tie Winding 2G, circuit 28, and receiver 32., while spacecurrent veriationsin seid tubes et frequencies other than the desiredfrequency, being out of phase with euch other, will neutralize euchothentliereby producing e very smell neghgibie 'etimt upon the retenerBy in phase with euchv heuppiied to the network.

'ceivers '43, or other adding more sections to the network, of the sumecharacter us sections 3, 8; Ll, E); etc., and connecting additional`repeating devices to the additional sections of the network in the samerelation as in the connections shown, the desired 'wuve frequency willbe further supplemented, while undesired frequencies will in general befurther neutralized in the common output circuit 2i AL though thecircuitdisclosed, when employingr only two repeaters such as 13, 14 inconjunction with the network 3, 8,; fi, 9; 5, 1U; provides e relativelyhigher degree of selectivity than the networks 3, 8; 4f, 9; 5, 10,alone, the circuit is mede more selective by adding sections 6, ll; 7,12, und rope-eter l5.

W'hen an impulse is impressed upon the network 2 from the source l, freeoscilla tions ure set up in the network in accordance with the naturelfree periods of the various closed circuits Which can Abe traced in thenetwork. rFliese free oscillation will, to e great ext-ent, be offrequencies which are different from that of the desired Wave frequency,sud for this reason, when any one frequency of the free oscillations isconsidered, the eli'ect thereof will be seen to be largely neutreiizedin the common output circuit 25 'by virtue of the dilierences in phaseof the potential waves seti upon the grids 18. The energy oii an impulseimpressed by the source l upon the network 2 is, therefore,discriminated against by the system es u whole, so that the disturbingenergy reaching;v receiver 32 is very small, or substantially zero,

lt is not essentiel that .impedance elements 3, et, 5, ,6, etc., be otequal value, or that impedance elements 8, il, 10, 11, l2, etc., beofequal velue, as in some euses it muy he desirable to use dili'erentvalues of said impednnces, for example., number of impedanccs ofdiii'erent values to function similarly to u, larger number ofimpedances of equul value.

to permit of e given y Fig. 2 illustrates uJ specific forni of networkin accordance with Figa l, particularly adept-ed to discriminate betweenin'ipulses and waives of some desired frequency and at the sume timeprovide e high degree of selectivity between the desired were frequencyund sli, other frequencies which muy flu this circuit, inductu-nccelements .35, ,33%, il?, et@ of' negli- ,cible rcsistuijufc, :areconnected in series with thesourcc of electr-emotivo force l. whilecapacities 40, 4l, ft2, etc., of negligible resistance, ect us shuntelements in the network 2. The capacities 40, 41, ctc., may beconsidered to include .the sti-uy capacities which in effectshunt thoseshown as, for example. the capacity between the grid 'und cathode Withina repeater.

receiving means respond to the desired News @ther parts of the Telep onere.

:atrapan circuit -are similar in structure und operation to thatdescribed in connection with Fig. 1. A. network of the type disclosed inFig. 2, may be designed in :u'corduncc with tithe disclosure in UnitedStates patent to G. A. Cam )bell No. 1,227, l

Fig. 3 s ows the selectivity of a circuit I having equal inductanceelements and equal capacity elements arranged similarly to Fig.

,10 l2having in this case a filler of eight sections,

four repeaters .beingl connected respectlvely across the second, fourth,sixth and eighth capacities counting from the source l and going in adirection away from said source.

'15 In this diagram the ordinate of u point on the curve respresents thesum of the grid potentials at a given frequency, while the vabscissa ofsaid point represents said `given frequency, it being'understood thatthe elec tromotive force of the source l is the saine .foreachfrequency. The point .45 corre-V sponds to thedesired frequency to bereceived. A Wave slightly above or below the Similarly, at other pointsthat corresponding to the point 45,

frequency corresponding to that of the point 45 is almostcompletelyneutralized, the ordinate corresponding: to the points 46 and 47 beingveryvsmall or substantially zero, ascompared to the ordinate of thepoint 45 corresponding to the desired frequency.

in the curve corresponding to maxima ofthe sum of the grid potentials.these sums are very small as compared with the sum at the point 45. Itwill thus be seen that at one frequency, namely, and at only this onefrequency, is there any appreciable effect produced upon the commonoutput circuit by the Vaction of the `grids. It order to obtain as higha degree of selectivity bv an ordinary selective circuit as is obtainedby the circuit of Fig. 2, the capacity and inductance elements requiredwould beof much more extreme dimensions than in the circuit shown.

Other forms of networks 0r filters than those shown in Fig. 2 mayobviously be utilized in accordance with this invention. For example,the source 1 may typify a source of received radio Waves, and thenetwork 2, an extended rudio antenna structure having distributed seriesinductauce and shunt capacity, or distributed series iiripedance of anyform, together ivith shunt An example of such an antenna structure isshown in United States patent to Lloyd-Espenschied No. 1,353,735.September 21, 1920.

' In Fig. 4: the network A. corresponding to the' `filters 2fof Figs. 1and 2 comprises an "antenna having lumped series i1npcdanceele- [ments LC. and lumped shunt impedance elements Lg. A source of received radiowaves 0 5 :sented bythe is represented by the broken arrow'. Shuntdistributed capacity ofthe antenna is repredottelf condenser-s whereasdiS- tributed series impedance is inherent in the conductors connectingthe lumped series impedanccs. The network AN is immatcrial, inV thisinvention and may he omitted it. desired.

The terms repeater andy repeating device`Y as employed herein are usedfor convenience to cover any form of unilateral device capable ofreproducing` in its output circuit, With or without magnification, anenergy change similar to the one impressed upon its input circuit, andmay produce in addition thereto, other energy changes than thoseimpressed upon the input circuit.

Although the invention has been disclosed showing;l grid coniuctions atpoints separated by two sections ot' a network, it is to be understoodthat one section or any desired number of sections may intervene betweenany two adjacent grid connections. Other modifications of the inventionthan those shown in the drawing,r are obviously dorniuated by thegenericprinciple disclosed herein. Features ol theu'nve'ntion which arebelieved to be novel are covered in the appended claims.

Vifhat is claimed is:

1. In a selective system, a source of electric waves, a plurality ot'repeaters controlled by said source, a network havingr a plurality ofsections connected between said repeaters and said source. saidrepeaters havingn individual input circuits connected toseparate pointsi-n said network in such manner that; for desired frequencies, theenergy supplied to respective repeaters is in phase, and for undesiredfrequencies the energy supplied to respective repeaters is out of phase,sired "frequencies is substantially excluded from an output circuitconnected to said repeaters.

' 2. In a selective system, a source of electrical waves, a plurality ofrepeaters as sociated therewith, and phase shifting means connectedbetween said source and said .lepeaters to applv to a plurality of saidrepeaters a wave of undesired frequency from said source in apluralityofdifferent hase relations with respect to the phase o said were appliedto one of said repeaters, and a connnon output circuitA associated withsaid repeaters to receive waves of desired frequency.

In a. selective system. a lsource of elec-4 of repeaters associ-lwhereby energy of said unde-v of said repeaters in ditferent phaserelationsA with respect to each other, and a commoii receiving circuitfor said repeaters.

"i, In a selective system, a source of electric waves, a plurality ofrepeaters associated therewith, and phase shitting means connectedbetween said" source and said repeaters to apply to each ot' saidrepeaters awave ot desired frequency from said source in the Asame phaserelation. and to apply waves ot' undesired frequencies' to cach of saidrepeaters in iliti'erent phase relations with respect to each other, acommon output circuit for said repeaters, 'and receiving meansassociated with said output circuit.

5. rl`he method' et selectively translating' et other repeatersiiulepemlently connected to Said network, each' at a diii'erentelectrical distance from said source than said lirstnamed repeater, anda common output en -Curt `for all of said repeaters.

7. The method oi increasingselectivityin the translation ot' electricenergy which comprises separatingT energy of undesired frequencies intoa plurality of components each having a dii'iiere'nt phase relation,combining said components to cause mutual .neutralization ot theireliects, and increasing the number of components ot said energy ofundesired frequencies suiipiciently to produce the desired selectivity.

8. In a selective system, a source of electric energy, a bilaterallyconducting circuit comprising a distribution ot' lumped series and shuntixnpedances connected to said source, a.plurality of repeaters greaterin' number than two, each independently connected to circuit at adiii'erent point therein and a. common outnit circuit for said rA`eaters.

a sclectivesystem, a souree'oii elec trie energy, circuit comprising a.distri bution of lumped series induetanee and shunt capacity connectedto said source, a

plurality of repeaters greater in number than two, each connected tesaid circuit at a different point therein, and aeommon output circuitfor said repeaters.

11G. in a selective system, a source of electric current, a circuitcomprising a distribution of series inductance and shunt capacityconnected to said source, a plurality ot' repeaters greater in numberthan two,

each connected to said circuit at a different bei' ot' repeaters andsections of said nets work may be indefinitely increased to improvetheoperation of the system, and common receiving means associated with saidrepeaters.

12. A receiving system comprising an input source'of energy, acontinuous homogeneous electrical network associated there- 4 with andcomposed of a plurality of sections serially connected, a plurality ofrepeating devices, greater in number than two, each connected to adilierent point` in said network, and common receiving means associatedwith said repeaters.

13. In combination, a plurality of electric,-

wave repeaters having separate input circuits and a common outputcircuit, a source of electric energy associated with said inputcircuits, and means provided between said source and said repeaters forimpressing undesired electric variations from said source uponsuccessive repeaters in successively diiif'erent phase relation, and forimpressing desired variations thereupon inthe same phase relation.

i4. ln combination, a plurality of electric Wave repeaters havingseparate input cix'-, cuits and a common output circuit, a source ofelectric energy associated with said input circuit, means providedbetween said source andv said repeaters for vimpressing undesiredelectric variations from said .source upon successive repeaters insuccessively different phase relation, and for im )ressing desiredvai-"tions thereupon in 't esame phase relation, and receivingmeans-assd' eiated with said common output circuit.

In witness whereof, I, hereunto subscribe ,my name this 27th day ofDecember, A. D.,

HAROLD iv. menons...

